The production of impregnated fibers and the application of thermoplastic resins to the fibers is well-known. Such fibers are coated with the thermoplastic resin after the fiber strand has been formed.
Sizing compositions typically employed as coatings for glass fibers have conventionally been applied to the surface of the glass fibers after the glass fiber has been formed. Typically it is necessary to first produce the glass fibers by providing a thin layer of a size composition to the surface of the bare glass fibers. The size composition must be compatible with the glass fiber and the resin which is subsequently applied to the sized fiber. The size composition serves to improve the bonding relationship between the glass fibers and the polymeric or thermoplastic resins. The glass fibers are then collected into a strand and the strand is wound around a take-up bobbin to form a substantially cylindrical package, conventionally termed a "yarn package". The yarn package is then air dried or subjected to elevated temperatures in order to dry the size composition applied to the surface of the glass fibers. The glass fibers are thereafter impregnated with the thermoplastic resin to form an impregnated yarn or cord.
However, it is difficult to produce a high performance thermoplastic impregnated glass fiber strand. Normally, the size composition include various processing aids which aid in improving the bonding relationship between the thermoplastic resin and the glass fibers. However, these processing aids remain in the impregnated strand. The processing aids are undesirable materials when clean thermoplastic impregnated glass fibers are desired, such as for use in producing high performance thermoplastic impregnated fibrous strand.
Considerable time and expense would be saved if a size composition useful for impregnating strands with a thermoplastic resin were available which could be applied during the fiber forming process without the need for non-aqueous solvents, fluidized beds, sheaths or time-consuming manufacturing processes.
Moreover, it would be beneficial if a size composition could be employed which, when directly blended with the thermoplastic resin during the glass fiber forming process, produces a substantially pure thermoplastic impregnated glass strand.